[johnta1]

The HEI pdf I posted in post #5 was from Horst Fiedler.

It has a lot of good info in it.

HEI PDF <- link again

[Schurkey]

Originally Posted by Schurkey

Some of the notes he posted were hand-written.

Originally Posted by johnta1

The HEI pdf I posted in post #5 was from Horst Fiedler.

It has a lot of good info in it.

HEI PDF <- link again

I guess I was wrong about some of the notes being hand-written.

[MatthewKlein]

Originally Posted by Kenth

Thanks to Schurkey:
https://www.gmcmi.com/wp-content/upl...stributors.pdf

Having read the thread I'm not quite sure if the Pole Piece is interchangeable between distributors or not.

If the white wire goes to the proper terminal it is?

[Schurkey]

Originally Posted by MatthewKlein

Having read the thread I'm not quite sure if the Pole Piece is interchangeable between distributors or not.

If the white wire goes to the proper terminal it is?

To my way of thinking, the "Pole Piece" is the star wheel that turns with the distributor shaft, with some relative motion due to the centrifugal advance (if equipped.) It has no wires.

The Pickup Coil has White and Green wires, that go to W and G terminals on the module.

There's three pickup coils for the usual V8 Coil-In-Cap HEIs with 4-pin modules. They're color-coded, and have different lengths of green and white lead wires. There's also two versions of magnetic polarity. They're NOT intended to be interchangeable, although some folks do.

This is a Pontiac-based web site, the Pontiac pickup coil has a white/clear, or no color coding, and has the longest lead wires, along with backwards magnetic polarity from the Yellow-coded pickup coil. (But same magnetic polarity as the Black/Blue pickup coil.) It would be used with the ignition coil-in-cap having red and white wires.

[Half-Inch Stud]

Yea, so if you have an original PMD coil, then that can be the "Gold Reference" for confirming others.

I'm certain the coil wind direction and the magnet polarity both have to be correct.

Whereas i'm pretty sure if you only got a Chevy pickup (with long enough wires) then a flipped magnet might bring the Pulse polarity to match the Pontiac.

The best verification is the check the pulse direction on a O'scope. Your HEI 4-pin module will thank you later.

[MatthewKlein]

Originally Posted by Schurkey

To my way of thinking, the "Pole Piece" is the star wheel that turns with the distributor shaft, with some relative motion due to the centrifugal advance (if equipped.) It has no wires.

The Pickup Coil has White and Green wires, that go to W and G terminals on the module.

There's three pickup coils for the usual V8 Coil-In-Cap HEIs with 4-pin modules. They're color-coded, and have different lengths of green and white lead wires. There's also two versions of magnetic polarity. They're NOT intended to be interchangeable, although some folks do.

This is a Pontiac-based web site, the Pontiac pickup coil has a white/clear, or no color coding, and has the longest lead wires, along with backwards magnetic polarity from the Yellow-coded pickup coil. (But same magnetic polarity as the Black/Blue pickup coil.) It would be used with the ignition coil-in-cap having red and white wires.

I have a distributor that needs a new one. We always just called the whole assy the pole piece, evidently incorrectly. Trying to find an original part and so far they are all chevy.

Swapping the chevy one it is a bad idea?

[MatthewKlein]

Originally Posted by MatthewKlein

I have a distributor that needs a new one. We always just called the whole assy the pole piece, evidently incorrectly. Trying to find an original part and so far they are all chevy.

Swapping the chevy one it is a bad idea?

My distributor is a 1976 bonneville 455 HEI
Does anyone know the original GM part number for the correct pickup coil

[Formulas]

I would like to know what the module does with the pole piece input, Does it use it as just a switch and if so how does polarity effect a switching on or off operation
Or does the module amplify the pole signal and the module cannot amplify a + when its expecting a - input at a certain time

I always viewed the module as sort of a relay using ultra low voltage created by pole piece to switch a higher power input to the coil to create the secondary circuit to create spark

[tc]

That's a good question. DUI sells one module to be used on different brand engines ( Pontiac, Chevy, etc. ) and wouldn't these engines would have different pickup coil polarity. Looks like they have one coil for different brand engine HEI's. It's confusing.

[Schurkey]

Originally Posted by MatthewKlein

I have a distributor that needs a new one... ...Trying to find an original part and so far they are all chevy.

Swapping the chevy one it is a bad idea?

Swapping a Chevy (yellow color-code) pickup coil into a Pontiac (white/clear, or no color code) is a bad idea. Among other problems, the wires are probably too short.

Go to ANY PARTS STORE IN AMERICA, order a pickup coil for your engine (or distributor). Stand there at the parts counter, take it out of the box, and verify that it has a clear/white, or NO color coded connector or tywrap on the wires. That should be correct for a PONTIAC application. These vehicles are getting old, but parts like this are still available.

Originally Posted by Formulas

I would like to know what the module does with the pole piece input, Does it use it as just a switch and if so how does polarity effect a switching on or off operation
Or does the module amplify the pole signal and the module cannot amplify a + when its expecting a - input at a certain time

I always viewed the module as sort of a relay using ultra low voltage created by pole piece to switch a higher power input to the coil to create the secondary circuit to create spark

Originally Posted by tc

That's a good question. DUI sells one module to be used on different brand engines ( Pontiac, Chevy, etc. ) and wouldn't these engines would have different pickup coil polarity. Looks like they have one coil for different brand engine HEI's. It's confusing.

Do not confuse MAGNETIC polarity with ELECTRICAL polarity. The magnetic polarity is different among engine families to reject RFI/EMP interference. The electrical polarity is the same at the module.

The module is the same for all engines. Even 4-pin four- and six-poppers. The module does not care which color-code the pickup coil is, because the White wire is attached to W, and the Green wire is attached to G no matter which pickup coil is being used.

There are crappy modules, and there are "high-performance" modules, and there's the good ol' reliable GM 990 module which may or may not be as good as what was being sold twenty+ years ago. But all 4-pin modules--good, or crappy--are intended to work with any color-code pickup coil. The module does not know the difference. (Because, electrically, there IS NO difference in the signal delivered to the module.)

The pickup coil output is a gradual voltage increase towards + voltage, a SUDDEN voltage decrease past "0" volts and into negative voltage, then another gradual voltage increase across "0" voltage into positive voltage. The SUDDEN voltage decrease across "0" voltage triggers the module to UN-ground the coil. That collapses the magnetic field of the coil, causing the spark.

As the pickup coil voltage begins to build toward + voltage, the module grounds the ignition coil allowing current flow through the primary windings, rebuilding the magnetic field in the ignition coil, and the process repeats. The module has additional circuitry to limit maximum current flow, along with variable-dwell circuitry which I'm not going to get into here.

So--dramatically simplified--the module acts as a relay, using the pickup coil signal as a trigger.

As for the different MAGNETIC polarity ignition coils...I have no idea. They exist, GM thought they were useful/needed, but no-one has been able to explain why, and I'm not bright enough to guess. Just like pickup coils, the MAGNETIC polarity is opposite, the ELECTRICAL polarity is EXACTLY THE SAME. MSD also sells only one version of in-cap ignition coil (Red and yellow--Chevy, Cadillac, Olds Toronado.) I don't think this is confusing, I think it's cost-cutting, inventory-reduction, and--maybe--ignorance/defiance/dontgiveashiit.

I'd use an in-cap coil with red and white wires on a Pontiac, because that's what GM specifies.

If you are not using an in-cap ignition coil, the magnetic polarity of the EXTERNAL coil does not matter.

[tekuhn]

I know this is an old thread, but I thought I'd add some information to it. I have been rebuilding a couple of Delco-Remy T.I./CD Ignition distributors and was searching for information related to the electrical polarity of the pickup coil that generates the magnetic pulse signal to trigger the module. The mag-pulse signal generated by the pickup assembly (coil, magnet, rotating pole piece (reluctor)) is an A/C signal. It is not a pure sine wave because the induced voltage increases as the pole pieces near alignment and immediately reverse as they begin to move away from each other. The time the signal is positive is shorter than the time it is negative. Therefore, the peak on the positive side is sharper and shorter in duration than the peak on the negative side which occurs in the dead space between poles.

I have HEI, TI, and MSD distributors available for testing, which provided some valuable information.

Since the magnetic pulse signal is an a/c voltage, referring a wire as positive or negative must be qualified as to WHEN it is positive or negative. I intend to refer to a wire as positive if it has a positive voltage on it as the pole pieces are approaching each other and swings negative as the pole pieces move apart. With this in mind - On an HEI pickup assembly, the GREEN wire is positive, and the white wire is negative. Following the same logic, on a TI distributor, the white w/green stripe is positive, and the white wire is negative.

Here's where it gets interesting. MSD says on their pickups, the black/orange (purple on extension) is positive and black/purple (green on extension) is negative. However, testing reveals that the wire MSD calls positive is going positive as the pole piece is moving AWAY from the coil. This is important if you try to use an MSD pickup to trigger an HEI module. You might be aware that MSD says for their products to use the pickup polarity that retards the timing the most with an older analog box and to use the polarity that gives the most advanced timing with the newer digital boxes. Clearly, the digital boxes trigger a spark as the "positive" wire swings negative (approaching) and the analog boxes trigger a spark as the "positive" wire swings positive (away).

Back to our GM products. Why does polarity matter? Two reasons come to mind. First is dwell time for coil saturation. Unlike capacitive discharge, HEI is still an inductive (Kettering) system just like a points setup. The length of time the ignition coil primary winding is energized is important to building a strong spark. Unlike a points system where the ignition coil is building a magnetic field charge anytime the points are closed, HEI always defaults to being off (points open) when there is no signal from the pickup coil. When you crank the starter and the distributor begins to spin, the pickup coil starts to generate a signal. As the signal pulse swings positive, the module connects the ignition coil primary to ground (equivalent to points closed) and the coil builds a magnetic field. As the positive pulse begins to drop (but it's still positive), the module opens the coil primary (equivalent points open) and the coils fires. If the polarity of the pickup signal is backwards, the positive peak is not the proper duration and the coil saturation timing is off. The other reason it matters is because of the rotor tip position. If the spark is occurring as the reluctor points are moving away from each other, the rotor tip is moving toward the zone in between plug wire contacts and misfires will happen.

I can't comment about different HEI pickup coils and 4-pin versus 7-pin modules. The HEI distributor I have is a 1977 unit and appears to have the original D-R 4-pin module.

Here is a link to a discussion on a different forum complete with oscilloscope wave patterns to illustrate what I was attempting to describe above....

https://www.slantsix.org/forum/viewtopic.php?t=56383

[TXSTARFIRE]

Interesting thread that I hadnt seen before, thanks for bringing it back up.

[70GS455]

Originally Posted by Ben M.

Distributor is on the front of the engine vs. the back like the others is the only noticeable difference.

Bias voltage being variable likely has to do with how easily triggered the system is at low vs. high RPM and the location on the B-H curve the system starts out at per pulse vs. RPM (note: this is an educated guess based on what I've done on pulsed systems I've designed).


I agree with everything you say now and have been saying. I use saturable reactors and high voltage charging inductors not unlike an automotive spark system in work and have for 20 years. This is why I have said I want to see voltage waveforms of everything to get a real idea of what is going on vs. what people say is happening. I 100% agree with Schurkey that GM went out of their way to specify the different pickup coils and ignition coils so obviously there was a reason, but I don't know what reason that was and I'm not 100% convinced on the story of the location of starter motor as that's many feet away and a simple DC motor - and as Schurkey pointed out doesn't hold true for FWD Olds and Buick.

Such a shame we don't have a line on anyone who worked in the ignition design on these cars, just some engineering notes or an interview or two would have gone a long way to answer these questions. And in agreement with George I'm sure a part of it is "this was the thing that stopped random hot start\stall\misfire issues so we shipped it as-is."

Old thread, but does this help?